Studies with rats have investigated the impaired utilization of alpha-tocopherol (vitamin E) when vitamin A is provided in the diet as retinoic acid rather than retinol. It was found that dietary retinoic acid inhibits the intestinal absorption of alpha-tocopherol and also promotes its oxidation to tocopheryl quinone. Retinoic acid had no effect on the excretin or composition of bile. The observation that the addition of bile acid to the diet reversed the inhibitory effect of retinoic acid on tocopherol absorption suggests that retinoic acid interferes with normal mixed nicelle formation. In other studies, the administration to rats of vitamins A and E intravenously in a total parenteral nutrition solution showed that these vitamins were efficiently stored in tissues and normal blood concentrations were maintained. The esterified form of vitamine E which was administered was completely hydrolyzed and only alpha-tocopherol was found in blood and liver.